1. Field of the Invention
The invention relates to rigid, closed cell foams and, in particular, to foams made with PVC backbones and epoxy-acrylated sidegroups crosslinked with diisocyantes and polymerized using photosensitive initiators.
2. Description of the Related Art
The preparation of compounds or mixtures with the purpose of manufacturing rigid foams on a PVC base is a very well known process that has been openly described in the scientific literature and in various international patents such as French patents Nos. 885,558 and 2,480,451 and U.S. Pat. Nos. 3,267,051 and 4,469,819. This, however, is completely different from the process described in this patent regarding both the compounds used and the development of the foam and cross-linking.
Recently, it has been discovered that polymer compounds or blends based on epoxy-oligomers react directly with isocyanates to form under certain chemical conditions (i.e. pressure, temperature, homogenization, etc.) a thermoplastic-thermofixed polymer. “Isocyanates” is a general term that is meant to include poly-isocanates as well as isocyanates, unless otherwise specified. These reactions take place only when these polymers or blends are subjected to elevated temperatures for relatively long periods of time. In contrast, when these blends are mixed at ambient temperature, the reactions described above do not take place because the conditions necessary for the generation of molecular excitation do not exist. There are also the epoxy-acrylates on the basis of diphenol A that react poorly in any temperature range.